Refrigeration-Type Dryer Apparatus and Method

ABSTRACT

A drying device includes an air/air heat exchanger and an air/refrigerant heat exchanger. The air refrigerant heat exchanger includes a phase change material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of and is a division of U.S. patentapplication Ser. No. 11/598,042, entitled “REFRIGERATION-TYPE DRYERAPPARATUS AND METHOD,” filed Nov. 13, 2006, now U.S. Pat. No. 7,721,787,which claims priority to and is a division of U.S. patent applicationSer. No. 10/670,213 entitled, “REFRIGERATION-TYPE DRYER APPARATUS ANDMETHOD,” filed Sep. 26, 2003, now U.S. Pat. No. 7,134,483, all of whichare hereby incorporated by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates generally to drying systems. Moreparticularly, the present invention is directed to a refrigeration-typeair dryer comprising a heat storage medium phase change material.

BACKGROUND OF THE INVENTION

Air dryers are generally utilized to remove water vapor typically fromcompressed air or gas. Where refrigerant-type air dryers are employed, arefrigerant system is used to lower the temperature of the air or gasbeing dried to a temperature at or below the condensation temperature ofwater therein. At such temperatures, water vapor in the undried aircondenses on a surface within a condenser where it can be collected andpurged from the system.

In order to sufficiently lower the temperature of the undried air orgas, many refrigerant systems comprise a heat exchanger where heat isdrawn from the air or gas being dried to a refrigerant. Typically, heatfrom undried air is coupled to the evaporation of a colder refrigerantin an evaporator. In this case, as the liquid refrigerant is vaporized,it removes heat from the undried air or gas and cools the air in theprocess. When the air or gas reaches a temperature at or below thecondensation temperature of water therein, the net result is that thewater vapor therein begins to condense (or separate) from the air or gasand is collected in a condenser or separator.

In order to recycle the refrigerant in the system, a compressor and achiller unit are often installed—the compressor compresses the gaseousrefrigerant that has been vaporized in the chiller, and the condensercondenses the gaseous refrigerant into a high pressure liquid. Therefrigerant is then ready for another cycle of vaporization.

A common problem with refrigeration-type dryers is determining how tosuspend cooling (i.e., “de-energize” the system) during times of no loador low load conditions. For example, the demand for refrigeration is lowor non-existent when little to no air is flowing through therefrigerator dryer or when the incoming air is already cool. Typically,it is desirable to reduce or discontinue cooling during such periods toavoid ice formation in the refrigerant system that could affectoperation of the refrigeration air dryer. Ice can plug the system sothat it does not continue drying the air, or it can plug the airpassages stopping the flow of compressed air.

One way to prevent excessive cooling and the resulting problem, is touse a cycling-type refrigeration dryer. In a cycling refrigeration-typedryer system, a thermostatic temperature device causes de-energizing ofa refrigerant compressor when the undried air has been cooled to apredetermined temperature. This can also be accomplished by measuringthe evaporator pressure. The same device can then cause the compressorto be re-energized when the temperature in the evaporator elevates to apredetermined temperature, indicating further cooling is required toremove moisture from the incoming air. Thus, it has been found thatbetween adequate load and low load conditions, a refrigerationcompressor may cycle on and off about thirty to forty times per hour.

The number of cycles per hour is significant because frequent cyclingadds costs associated with wear and tear on the compressor, controlsystems, and valves. As a result, the life without maintenance of therefrigeration system is drastically reduced. Accordingly, it would bedesirable to provide a refrigerant air dryer system and method thatextends the life of its refrigeration system.

Moreover, the greater the number of times a refrigeration system cycles,the greater the amount of energy that is consumed. Lower energyconsumption has both cost and environmental benefits. Accordingly itwould also be desirable to provide a refrigeration dryer system andmethod that reduces the amount of energy consumed.

SUMMARY OF THE INVENTION

The foregoing needs are met, to an extent, by the present invention,wherein in one embodiment an air drying apparatus is provided thatcomprises a refrigerant system and a heat exchanger further comprising aphase change material, wherein the refrigerant system is adapted forcooling the heat exchanger. The air dryer may dry air or gas which mayoptionally be compressed air or gas. In some embodiments, air dryers ofthe present invention may comprise a condensate separator, preferablyincluding a wire mesh. The phase change material can change betweensolid and liquid phases. In some embodiments the phase change materialis an organic paraffin.

In other embodiments, a method of drying air is provided which comprisesproviding a refrigerant system and a heat exchanger comprising a phasechange material and using the refrigerant system to cool the heatexchanger. The method may be used to dry air or gas which may optionallybe compressed air or gas. In some embodiments, method of air drying ofthe present invention may comprise a condensate separator, preferablyincluding a wire mesh. The phase change material can change betweensolid and liquid phases. In some embodiments the phase change materialis an organic paraffin.

In yet other embodiments, a means for drying air is provided, comprisinga refrigeration means and a heat exchanger means comprising a phasechange material, wherein the refrigeration means is adapted for coolingthe heat exchanger means. The air drying means may dry air or gas whichmay optionally be compressed air or gas. In some embodiments, air dryermeans of the present invention may comprise a condensate separatormeans, preferably including a wire mesh. The phase change material canchange between solid and liquid phases. In some embodiments the phasechange material is an organic paraffin.

There has thus been outlined, rather broadly, the more importantfeatures of the invention in order that the detailed description thereofthat follows may be better understood, and in order that the presentcontribution to the art may be better appreciated. There are, of course,additional features of the invention that will be described below andwhich will form the subject matter of the claims appended hereto.

In this respect, before explaining at least one embodiment of theinvention in detail, it is to be understood that the invention is notlimited in its application to the details of construction and to thearrangements of the components set forth in the following description orillustrated in the drawings. The invention is capable of otherembodiments and of being practiced and carried out in various ways.Also, it is to be understood that the phraseology and terminologyemployed herein, as well as the abstract, are for the purpose ofdescription and should not be regarded as limiting.

As such, those skilled in the art will appreciate that the conceptionupon which this disclosure is based may readily be utilized as a basisfor the designing of other structures, methods and systems for carryingout the several purposes of the present invention. It is important,therefore, that the claims be regarded as including such equivalentconstructions insofar as they do not depart from the spirit and scope ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cut-away of an evaporator of a refrigerated air dryer inaccordance with the present invention.

FIG. 2 is a cut-away of refrigeration chiller of a refrigerated airdryer in accordance with the present invention.

FIG. 3 is a cut-away of refrigeration chiller of a refrigerated airdryer in accordance with the present invention.

FIG. 4 is cut-away of refrigeration chiller of a refrigerated air dryerin accordance with the present invention. in accordance with the presentinvention.

DETAILED DESCRIPTION

The invention will now be described with reference to the drawingfigures, in which like reference numerals refer to like partsthroughout. An embodiment in accordance with the present inventionprovides a refrigeration system 10 operationally coupled to a heatexchanger 20 to cool undried compressed air to a temperature sufficientto separate and remove any water therein by virtue of its condensationat such sufficient temperature. The heat exchanger 20 may be of multipleembodiments, some of which will be described below. In the schematicshown in FIG. 1, the heat exchanger 20 comprises an air-to-air(“air/air”) exchanger 30 and an air-to-refrigerant (“air/refrigerant”)exchanger 40. The exchanger 40 further comprises a thermal jacket 50,which in the embodiment shown, is directly cooled by the refrigerantsystem 10. The exchanger 30 is shown with co-current flow in FIG. 1, butin some embodiments can also comprise counter-current flow.

Broadly speaking, air, gas, including compressed air and gas, orgenerally, any vapor in need of drying, is injected into the heatexchanger 20 through an inlet 60. The term “air” has been used herein toencompass all of the above fluids and should not be construed or limitedto any one particular embodiment. The air then travels through theexchanger 30 to the exchanger 40. Preferably, the air traverses a path61 through the exchanger 30, adapted in a manner such that heat from thehotter, undried air entering the inlet 60 can be transferred to thecooler, dried air exiting an outlet 70. By way of example, air enteringthe inlet 60 may be 40 to 70 degrees Fahrenheit hotter than air exitingthe outlet 70. Such a temperature differential can provide motive forsignificant heat transfer without the need for further mechanicalintervention.

Once the air has traversed the exchanger 30, it enters the exchanger 40.The exchanger 40 is designed to draw heat from the incoming air to therefrigerant 11 supplied by the refrigerant system 10. In the embodimentshown, the refrigerant 11 cools the thermal jacket 50. Contents of thethermal jacket may comprise any material known and present in the artthat can be cooled to a temperature at or lower than the dew point ofthe vapor (i.e., water) being condensed. Suitable materials include, butare not limited to, glycols and mixtures thereof.

In some embodiments, the thermal jacket 50 may comprise a phase changematerial (PCM). PCMs are heat storage media that can absorb or diffuseheat by changing from a solid to a liquid, or vice versa. In the instantinvention, for example, as the phase change material absorbs heat fromthe undried air, it begins to change phase from a solid to a liquid.However, without being limited by or held to scientific theory, becauseof the constant temperature behavior of PCM technology, the thermaljacket 50 can maintain a constant temperature during the transition. Theprocess can take minutes to hours depending on the PCM, ambienttemperature of the air, and workload.

In some embodiments, PCMs that can absorb the greatest amount of heatover the smallest temperature range are preferred. In other words, PCMsthat remain in the solid phase longer for a given amount of heat aredesirable. Scientifically, the thermal conductivity of a fluid increasessignificantly when in a solid phase as opposed to a liquid. Water, forexample, has a thermal conductivity of 0.326 BTU/hr-ft-° F. at 32° F.,whereas ice has a thermal conductivity of 1.18 BTU/hr-ft-° F. at thesame temperature. Because of their ability to absorb heat at both asolid state (high thermal conductivity) and a liquid state (lowerthermal conductivity), PCMs can more rapidly and efficiently absorb theheat of condensation than materials that do not undergo a phase change.Therefore, much more heat can be stored in a much smaller volume ofmedium using the latent heat of freezing (solid→liquid) rather than theheat associated with changing temperatures, allowing for the developmentof much smaller heat exchangers.

During standard operation of one embodiment of the instant invention,the refrigerant 11 cools (or “charges”) the thermal jacket 50 so thatthe PCM therein becomes solid, thereby allowing the thermal jacket 50 todraw heat from the incoming air 61. The heat from the incoming air 61 istransferred through the PCM/thermal jacket 50 to the heat absorbingrefrigerant 11.

When the temperature or pressure of return refrigerant 12 reaches apre-determined temperature or pressure, the refrigerant system 10 canshut off. The pre-determined temperature or pressure may be chosen tosignal that no further cooling by the refrigerant system 10 is needed,for example, at times when the temperature or pressure of refrigerant 11entering the thermal jacket 50 nears the temperature or pressure of therefrigerant 12 exiting the jacket 50.

During such periods of little to no load, when the compressor isdeenergized, the PCM can continue to absorb heat from the undried air.In other words, the PCM can supply the necessary cooling by absorbingheat in the solid phase while maintaining a low constant temperaturebefore changing to liquid. In such a manner, this invention can allowfor the extension of time periods where the refrigerant system 10 mayremain deenergized

When the temperature of return refrigerant 12 or the thermal jacket 50reaches a pre-determined temperature, the refrigerant system 10 canre-energize and the PCM can be relatively quickly recharged (i.e.,solidified) by the refrigerant system 10. The net effect of this systemis that the cycle periods can be extended and less energy can beconsumed than convention refrigeration-type air dryers that do not usePCMs. The compressor cycling rate can be reduced from thirty or fortytimes per hour to, for example, less than six per hour.

Heat storage mediums can be developed to change state at a chosentemperature. For example, a medium can be of a composition to freeze at+4° C. that would preclude water freezing, or icing, in the exchanger40. PCMs which change states between liquid and solid are manufacturedby many companies, for example PCM Thermal Solutions of Naperville, Ill.The PCM A4 is an organic paraffin which freezes at +4° C. and iscomposed of a blend of heavy cut hydrocarbons. The types E7 and E8 thatchange state at +7° C. and +8° C., respectively, are composed of ammoniaand sodium sulfate salts. For low dew point services, such asrefrigeration systems with reversing regenerative heat exchangers, lowtemperature PCMs can be used including TEA-29 that freezes at −29° C.The TEA media are composed of inorganic hydrated salt solutions, such ascalcium chloride in water.

Returning to FIG. 1, the cooled air 62 exiting the thermal jacket 50,should be cooled enough to initiate condensation of the water therein.The use of “water” herein is merely exemplary, and is intended toinclude any and all vaporous fluids that are chosen for condensation.The condensed water, then, is collected and removed in a condensateseparator 80. Condensate separators are known in the art and any suchseparator may be used with the present invention.

As shown in FIG. 1, the return path for cooled air 62 may optionally beadapted in the exchanger 30 such that heat may be transferred from theincoming air 61 to the exiting air 62. In such a way, not only is theexiting air heated closer to the temperature of the air 61 as it entersthe exchanger 20, but the air 61 entering the exchanger 20 is precooledbefore entering exchanger 40.

A conventional refrigeration system 10 is depicted in the embodiment ofFIG. 1. Refrigerant gas 12 is pressurized by a compressor 13. Thecompressor 13 compresses the refrigerant gas 12. The compression processraises the refrigerant 12 pressure and also the temperature. In order tocool the temperature, the refrigerant 12 is channeled through acondenser 14, which is a heat exchanging means that allows therefrigerant 12 to dissipate the heat of pressurization. As it cools, therefrigerant gas 12 cools into a refrigerant liquid 11. The refrigerant11 is then dried and/or filtered of contaminants by a filter/dryer means15.

The liquid refrigerant 11 is then passed through an expansion device 16which transfers the liquid refrigerant 11 from a high pressure zone to alow pressure zone, thereby vaporizing the refrigerant 11. Inevaporating, the refrigerant 11 draws heat, preferably from the thermaljacket 50 and/or the undried air 61. Typically, refrigeration systemswill also comprise a sensing bulb 17. The sensing bulb 17 is generally atemperature sensing device that can regulate the flow of the returnrefrigerant 12. Preferably, the sensing bulb 17 is able to compare thetemperature of the cooled refrigerant 11 with the return refrigerant 12and has the means to regulate the system 10 when a pre-determinedsuperheat is reached.

Shown in FIG. 2 is an embodiment of a heat exchanger 120 in accordancewith the present invention. The heat exchanger 120 comprises an air/airheat exchanger 130, an air/refrigerant heat exchanger 140, and acondensate separator 180. The air/refrigerant exchanger 140 is known asa “brazed plate” heat exchanger and comprises a series of stackedplates. The plates may be comprised of any materials that are sturdywhen pressurized, heated, and cooled, and can conduct heat efficiently.Preferably metal plates are used, and more specifically, stainless steelor copper plates.

A braised plate exchanger comprises alternating stainless steel andcopper plates fused together creating “gaps” or “slits” between theplates. In some embodiments of the present invention, at least threesuch gaps are envisioned. A first of the gaps is utilized to contain anincoming flow of air to be dried. A second of the gaps can contain arefrigerant and a third one of the gaps may contain a PCM. Preferably,the refrigerant plate contacts the PCM plate which contacts the airplate, however, alternate combinations are also possible.

As shown in FIG. 2, an inlet pipe 160 may be attached to the air/airexchanger 130 evaporator to allow incoming air to flow into any chamberdesignated to hold incoming air. Preferably, as described above, theincoming air follows a course counter-flow to the outgoing air. Thisadaptation functions as an air/air heat exchange thereby pre-cooling theincoming air before it enters exchanger 140. The incoming air then movesthrough the braized plate heat exchanger 150.

The braized plate heat exchanger 150 comprises a series of stackedplates creating chambers therefrom. For the reasons mentioned above, theincoming air preferably traverses the heat exchanger 140 counter-flow tothe refrigerant. A probe 155 may also be incorporated in the exchanger150 to sense and/or report a status of the refrigerant and/or the PCMtherein. Preferably, in some embodiments, the probe 155 is a phasechange temperature sensing probe and is located at a location withinexchanger 150 where the PCM would be warmest. However, probe 155 may beadapted for use in any location within heat exchanger 120. In any event,once having traversed the heat exchanger 140, the exiting air is cooledto permit condensation of the water.

A condensate separator 180 may be coupled to the exchanger 120 via anoutlet port 190. The separator 180 separates the condensed water fromthe air stream. In some embodiments, a mesh 181 may be introduced intothe separator 180 to aid condensation. The mesh 181 may comprise anymaterial, preferably materials that will not rust or fail when wet, andneed not be limited to any one particular design. Stainless steel wiremeshes may be utilized in some embodiments. A drain 182 may be providedto allow the condensate to exit the separator 180.

Piping 100 may be coupled to the separator 180 to allow dried air tore-enter the exchanger 130, and exit through an outlet port 170. Anair/air exchanger 130 is provided to allow the outgoing cool dry air topre-cool incoming warm air.

Shown in FIG. 3 is an embodiment of a heat exchanger 220 in accordancewith the present invention. The heat exchanger 220 comprises an air/airheat exchanger 230, an air/refrigerant heat exchanger 240, and tubes 221and 222 that permit that transfer of air between the exchangers 230 and240.

In greater detail, the heat exchanger design of FIG. 3 comprises aninlet port 260 that receives an incoming flow of a fluid, for example,compressed air. The inlet 260 is coupled to tubing 231 within exchanger230 that is adapted for air/air heat exchange between the warmer,undried air entering the exchanger 220 and the cooler, dried air exitingthe exchanger 220. For example, air entering may be designed to flowthrough the tubes 231 through the center or periphery of exchanger 230,the sum of the tubes 231 being surrounded by cooler air exiting anoutlet 270. As with the other embodiments described herein, preferably,the entering air and the exiting air are arranged in a counter-flowarrangement so as to maximize heat transfer. Such designs are commonlyreferred to as “shell-and-tube” or “multitube-in-tube” heat exchangersin the art.

Once the incoming air has traversed the air/air exchanger 230, it maymove through a connecting tube 221 into the air/refrigerant exchanger240. The exchanger 240 can be constructed with three concentric tubessuch that the refrigerant flows through the inner-most tube, a PCM isretained between the first and second tube, and the air passes throughthe annular space between the third and second tubes. The triple tubedesign can be constructed in a coiled manner, or it can be designed as astraight tube construction as shown. Refrigerant is circulated throughthe exchanger 240 through inlet/outlet ports 241. The refrigerant, inturn, cools a jacket 245 containing the PCM and/or the undried airtraversing the exchanger 240.

As heat is drawn from the incoming air to the refrigerant and/or thePCM, the air is cooled to or below its dew point and moisture (e.g.,water) begins to condense. The condensed water is collected within theexchanger 240 and can be drained from the system though a condensatedrain 242. The exchanger 240 may also include a fluid fill/vent 243. Thefill/vent 243 may be adapted to allow filling or refilling of PCM as isrequired, and also allow for venting of gases or heat contained therein.

Preferably, in some embodiments, a probe 243 is incorporated into theair/refrigerant exchanger 240. Preferably, the probe 243 is a phasechange temperature sensing probe and is located at a location within theexchanger 240 where the PCM would be warmest. However, the probe 243 maybe adapted for use in any location within heat exchanger 120. The probe243 may also signal shut-off or operation of the refrigerant system insome embodiments.

In the embodiment shown in FIG. 3, once dried, the cooled air may bedirected by another connecting tube 222 back to the exchanger 230. Inthe arrangement shown, the cooled air is fed counter-flow to theincoming air in tubes 231 within the exchanger 230. This process notonly cools air within the tubes 231, but also warms the dried airexiting the exchanger 220 though the outlet 270.

FIG.4 depicts a heat exchanger 320. The heat exchanger 320 comprises anair/refrigerant exchanger 340 and a separator 380, and may optionallyinclude an air/air exchanger as well. The exchanger 340 can beconstructed with three coiled tubes bundled together as illustrated inthe figure. One of the three tubes 361 passes the air as it enters theexchanger 320 and exits drier. The air may enter/exit the exchanger 320via an inlet/outlet 365 which can comprise a tube within a tube design.

In addition, there are at least two other tubes 311 and 351positioned/nested around the air tube 361. One of the other tubes, 351,contains a PCM, and the other of the two tubes, 311, contains arefrigerant. In the preferred embodiment of the present invention, thetubes 311, 351, and 361 are made from copper, and all three tubing linesare positioned such that one line of tubing does not overlap anotherline of material.

However, it should be understood by one of ordinary skill in the artthat the three lines of tubing may all be made from any other material,or each of the three lines of tubing may be made from differentmaterials. It should also be understood by one of ordinary skill in theart that the positioning of the three lines of tubing may also vary.

The exchanger 320 embodied in FIG. 4 additionally comprises a separator380 to mechanically separate the condensed moisture from the dried air.A probe 355 may also be installed in the exchanger 320 as indicated inthe embodiments above.

The many features and advantages of the invention are apparent from thedetailed specification, and thus, it is intended by the appended claimsto cover all such features and advantages of the invention which fallwithin the true spirit and scope of the invention. Further, sincenumerous modifications and variations will readily occur to thoseskilled in the art, it is not desired to limit the invention to theexact construction and operation illustrated and described, andaccordingly, all suitable modifications and equivalents may be resortedto, falling within the scope of the invention.

1. An air/refrigerant heat exchanger, comprising: a plurality of coiledtubes; a first tube of the plurality of tubes, the first tube having aphase change material therein; a second tube of the plurality of tubes,the second tube having a flow of cooled refrigerant flowingtherethrough, the first tube being in thermal contact with the secondtube; and a third tube of the plurality of tubes, the third tube havinga flow of air flowing therethrough, the third tube being in thermalcontact with the first tube and the second tube.
 2. The air/refrigerantheat exchanger of claim 1, further comprising a condensed moistureseparator.
 3. The air/refrigerant heat exchanger of claim 2, furthercomprising: an air inlet configured to receive a flow of warm moist air.4. The air/refrigerant heat exchanger of claim 3, wherein the third tubeconveys the flow of air from the air inlet to the condensed moistureseparator.
 5. The air/refrigerant heat exchanger of claim 4, furthercomprising: a fourth tube disposed within the third tube, the fourthtube being configured to convey of air from the condensed moistureseparator.
 6. The air/refrigerant heat exchanger of claim 1, furthercomprising a probe.
 7. The air/refrigerant heat exchanger of claim 6,wherein the probe is configured to sense a temperature of the phasechange material.
 8. The air/refrigerant heat exchanger of claim 3,further comprising: an air/air heat exchanger.
 9. The air/refrigerantheat exchanger of claim 8, wherein the air/air heat exchanger isdisposed upstream of the air inlet, the air/air heat exchanger beingconfigured to initially cool the flow of warm moist air.
 10. Theair/refrigerant heat exchanger of claim 1, wherein the first tube, thesecond tube and the third tube are copper.
 11. An air/refrigerant heatexchanger, comprising: a thermal reservoir tube having a phase changematerial therein; a cooling tube having a flow of cooled refrigerantflowing therethrough, the thermal reservoir tube being in thermalcontact with the cooling tube; and an air tube having a flow of airflowing therethrough, the air tube being in thermal contact with thethermal reservoir tube and the cooling tube.
 12. The air/refrigerantheat exchanger of claim 11, further comprising a condensed moistureseparator.
 13. The air/refrigerant heat exchanger of claim 12, furthercomprising: an air inlet configured to receive a flow of warm moist air.14. The air/refrigerant heat exchanger of claim 13, wherein the air tubeconveys the flow of air from the air inlet to the condensed moistureseparator.
 15. The air/refrigerant heat exchanger of claim 14, furthercomprising: a return air tube disposed within the air tube, the returnair tube being configured to convey of air from the condensed moistureseparator.
 16. The air/refrigerant heat exchanger of claim 11, furthercomprising a probe.
 17. The air/refrigerant heat exchanger of claim 16,wherein the probe is configured to sense a temperature of the phasechange material.
 18. The air/refrigerant heat exchanger of claim 13,further comprising: an air/air heat exchanger.
 19. The air/refrigerantheat exchanger of claim 18, wherein the air/air heat exchanger isdisposed upstream of the air inlet, the air/air heat exchanger beingconfigured to initially cool the flow of warm moist air.
 20. Theair/refrigerant heat exchanger of claim 11, wherein the air tube, thethermal reservoir tube and the cooling tube are copper.